The present invention relates to matrix-addressable displays, and more particularly, to column and row line formation of control circuits in matrix-addressable displays.
Matrix-addressable display are widely used in a variety of applications, including computer displays. One type of display well suited for such applications is the field emission display. Field emission displays typically include a generally planar baseplate positioned beneath a faceplate. The baseplate includes a substrate having an array of emitters. Usually, the emitters are conical projections integral to the substrate and grouped into commonly connected emitter sets.
The baseplate also includes a conductive extraction grid positioned above the emitters and driven with a voltage of about 30-120 volts. The emitters are selectively activated by providing electrons to the emitters, for example by grounding the emitters. If the voltage differential between the emitters and the extraction grid is sufficiently high, the resulting electric field extracts electrons from the emitters.
The faceplate is mounted adjacent the extraction grid and includes a transparent display screen coated with a transparent conductive material to form an anode that is generally biased to about 1-2 kV. A cathodoluminescent layer covers the exposed surface of the anode. Electrons emitted by the emitters are attracted by the anode and strike the cathodoluminescent layer, causing the cathodoluminescent layer to emit light at the impact site. The emitted light then passes through the anode and the glass plate where it is visible to a viewer. The brightness of the pixel produced in response to the emitted electrons depends, in part, upon the number of electrons striking the cathodoluminescent layer in an activation interval, which in turn depends upon the current flow from the emitters. The brightness of each pixel can thus be controlled by controlling the current flow from the respective emitter or emitter set. The light from each area of the display can thus be controlled to produce an image. The light emitted from each of the areas thus becomes all or part of a picture element or xe2x80x9cpixel.xe2x80x9d
In practice, the emitters are usually arranged in columns, while individual extraction grids are arranged in rows. An individual emitter can then be selected for electron emission by driving a column of emitters to a relatively low voltage and driving an extraction grid row to a relatively high voltage. Electrons are emitted from the emitter in the energized column of emitters that intersects with the energized extraction grid row.
The columns of emitters and the rows of extraction grids are typically driven by metal column lines and row lines, respectively, formed on a single substrate. Usually, the column lines and row lines are formed at right angles to one another. The column lines in a first plane are spaced from the row lines in a second plane and separated from each other by a layer of dielectric material. The emitters are may be formed at the points of intersection where the column lines and row lines cross. The column and row lines and intermediate dielectric produces a capacitive effect leading to relatively large RC time constants in the drive circuit.
The present invention is directed to apparatus and methods in matrix-addressable displays for reducing the overlap between conductive portions of the column and row lines while maintaining the nominal widths of the conductive lines.
In one aspect of the invention, the matrix-addressable display includes a number of conductive column lines, each having a number of windows or openings. A window underlies each intersection where a conductive row line overlaps or crosses the column line. Each of the windows has a width that is less than the width of the column line and a length that may be greater than the nominal width of the row line crossing the column line. A conductive layer of a doped semiconductor, such as doped polysilicon, overlaps each of the windows and is electrically coupled to the column line. The doped semiconductor may carry a number of emitters and provides a current path between the emitters and the column lines.
In another aspect of the invention, the matrix-addressable display includes a number of conductive row lines spaced from and crossing or intersecting the column lines at a number of locations. Each of the row lines includes a number of windows or openings. The windows may be positioned at each location where the row and column lines overlap. Each of the windows or openings may have a length greater than a nominal width of the column line that the window overlays. A conductive, doped semiconductor layer overlaps each of the windows in the row line and is electrically coupled thereto. A number of apertures may be formed in the doped semiconductor layer, each of which is aligned with ones of the respective emitters to form an extraction grid.
A layer of dielectric material may separate the semiconductor supporting the emitters and the row lines to space the row lines from the doped semiconductor carrying the emitters and to electrically isolate the column lines from the row lines.
The windows in the row and column lines may be sized, dimensioned, and positioned to reduce the area of overlap of the metal portions of the column and row lines while maintaining the nominal widths of the lines. Thus, the RC time constant may be reduced where resistance is inversely proportional to line width and capacitance is directly proportional to overlap area.